Greases thickened with sodium salts of alkyl mercapto fatty acids



United States Patent Ofitice 3,048,541 Patented Aug. 7, 1962 3,048,541 GREASES TTHCKENED WTTH SUDHJM SALTS F ALKYIL MERCAPTi) FATTY ACIDS Johan (I. D. Dosterhout, Port Arthur, Tern, assignor to Texaco Inc, a corporation of Delaware No Drawing. Filed Apr. 29, 1957, Ser. No. 655,465 6 Claims. (Cl. 252-33.6)

This invention relates to improved lubricating greases and more particularly to greases thickened with sodium soaps of alkyl mercapto fatty acids.

The alkyl mercapto fatty acid soaps which are employed for thickening lubricating greases in accordance with this invention are represented by the formula RSR COONa, wherein R and R are substantially straight chain alkyl groups each containing from 1 to about 20 alkyl carbon atoms and wherein R and R together contain about 11-30 alkyl carbon atoms. By substantially straight chain alkyl group is meant an alkyl group containing not more than one tertiary or quaternary carbon atom and having no side chains containing more than two carbon atoms. The preferred compounds are those wherein R is an alkyl group containing about 820 carbon atoms and R is an alkyl group containing about 1-5 carbon atoms. Specific examples of compounds. of this preferred type include sodium octadecyl mercapto acetate, sodium octyl mercapto caproate and sodium lauryl mercapto propionate.

I have found that, contrary to the experience with other soaps of similar sulfur-containing fatty acids, the above soaps thicken lubricating oils very successfully so as to produce lubricating greases in good yields, and that the greases thus produced have very superior lubricating properties which are not obtainable by employing the conventional fatty acid soaps as grease thickening agents. They are characterized particularly by a combination of high load carrying capacity, not obtainable in the conventional sodium base greases without the use of additives, and very superior anti-corrosiveness to metals.

The alkyl mercapto fatty acids which are employed for forming these soaps may be prepared by any convenient method, such as, for example, by the method of Kharash and Fuchs, Journal of Organic Chemistry, vol. 13, page 97 (1948), which involves reacting a mercaptan with an unsaturated fatty acid ester in the presence of a strong alkali, and hydrolizing the product. Other methods which may be employed include reacting a sodium mercaptide with a halogen substituted organic acid, or reacting a mercaptan with an unsaturated nitrile such as acrylonitrile and then hydrolizing in the presence of sodium hydroxide so as to produce the sodium soap directly.

The lubricating oils employed in these greases may be any oleaginous liquids suitable for use in grease making generally, such as mineral oils obtained by any of the conventional refining processes in the lubricating oil viscosity range, preferably those having viscosities vfrom about 80 seconds Saybolt Universal at 100 F. to about 225 seconds at 210 F. Refined mineral oils having viscosities in about the range 100 to 600 seconds Saybolt Universal at 100 F. are particularly suitable. For some purposes, as for preparing greases for high temperature operations, various synthetic oils may be employed with advantage, such as, for example, polyalkylene glycols, high molecular weight esters and ethers, and silicone polymer oils. Especially suitable synthetic oils are the dicarboxylic acid esters described by R. T. Sanderson in US. 2,628,974. Such synthetic oils may be employed as the sole oleaginous liquid component, or in admixture with other synthetic oils or with mineral oils in various proportions.

The sodium alkyl mercapto fatty acid soaps described above are employed in the mineral or other lubricating oils in sufiicient amounts to impart a grease consistency to the composition, generally in an amount above about 10 percent by Weight, and preferably in an amount from about 15 to about 45 percent by weight, based on the weight of the composition.

Additives of the usual types may be employed in these greases, such as oxidation inhibitors, corrosion inhibitors. tackiness agents, such as various high polymer materials, extreme pressure agents, and so forth. Suitable oxidation inhibitors include phenyl alpha naphthylamine, diphenyl para-phenylamine diamine, tetramethyldiaminodiphenylmethane and his (2-hydroxy-3 tert.-butyl-5-methylphenyl)methane. In addition, the greases may contain other thickening agents such as finely divided solids or other metal soaps such as sodium, lithium, calcium, etc., or mixed base soaps of stearic acid or other long chain fatty acids or hydroxy fatty acids.

The following example is given for the purpose of further disclosing the invention.

Example A grease representative of the grease compositions of this invention was preparedhaving the following composition in percent by weight:

Na lauryl mercapto propionate 17.0 Phenyl alpha naphthylamine 0.44 Mineral lubricating oil Remainder The mineral lubricating oil employed in the grease was a refined naphthenic distillate oil having a Saybolt Universal viscosity of 310 seconds at 100 F.

The sodium lauryl mercapto propionate was obtained by saponification of the mercapto acid prepared by the method involving reacting lauryl mercaptan with methyl acrylate in the presence of caustic, and then hydrolizing. The method in detail was as follows: 380 grams of lauryl mercaptan and 200 grams of methyl acrylate were introduced into a flask and 5 grams of sodium were added gradually. The mixture was allowed to stand for one hour at l00 C. to complete the reaction. The product was hydrolized by adding 250 ml. of 20 percent aqueous sodium hydroxide and 750 ml. of ethyl alcohol and allowing the mixture to stand for one hour. The mixture Was then acidified with hydrochloric acid and the reaction product filtered off and washed with water. The product melted at 35-42 C. and had a neutralization number of 101 and a sulfur content of 10.2 percent.

The grease preparation was carried out in the following manner: 475 grams of the lauryl mercapto propionic acid, 475 grams of the mineral oil and 137 grams of 50 percent aqueous sodium hydroxide were charged to a laboratory grease kettle and the reaction mixture heated at 200 F. for one hour until the saponification was complete. The mixture was then heated at 300 F. for an additional hour to dehydrate. While the mixture was at about 300 R, an additional 475 grams of mineral oil were added, and an additional 1425 grams of mineral oil were added gradually during cooling from about 300 F. to about 180 F. When the mixture had cooled to about 200 F, 12.8 grams of phenyl alphanaphthylamine were added. The grease was finally drawn at 180 F.

The grease obtained as described above was a smooth buttery grease of good texture and appearance. Inspection data on this grease are given below.

Penetration, ASTM, at 77 F.:

Norma-Hoffmann oxidation test, hrs.,

210 F., lbs. pressure drop 3 3 Copper corrosion test, AN-G-ZS method,

24 hours, 212 F. Passes Mean Hertz load 31.1

The Mean Hertz load test is a Well-known laboratory test for determining the load carrying capacity of lubricating compositions. It is carried out as described, for example, in U.S. 2,600,056, column 12, lines l360, employing a test machine which comprises four steel balls in a pyramid arrangement and lubricated at their points of contact with the lubricant under test. The test comprises rotating the upper ball at a high speed in contact with the lower three balls, while a load is applied to the system by means of a lever arm. The Mean Hertz load is the load upon the lever in kilograms which causes welding after ten seconds of operation. Mean Hertz loads of about 20 are obtained with the conventional sodium base greases.

As shown by the above data, the grease representative of the greases of this invention had a very substantially improved load carrying capacity as compared with the conventional sodium base greases, and in addition it was non-corrosive to copper in the copper strip corrosion test at 212 F. This combination of properties is not obtainable in greases prepared from the conventional fatty acids without the use of additives, and in addition it is not obtained by employing other metals as the metal component of the the mercapto fatty acid soap. In addition to this desirable combination of properties, the greases of this invention have very satisfatcory shear stability, good inhibitor response, high dropping points, and other desirable lubricating properties.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made Without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A lubricating grease consisting essentially of a luaoaaeea bricating oil thickened to a grease consistency with a sodium alkyl mercapto fatty acid salt having the formula RSR COONa, wherein R is a substantially straight chain alkyl group containing about 8 to 20 carbon atoms and R is a straight chain alkylene group containing from 1 to 5 carbon atoms, and wherein R and R together contain about aliphatic 11 30 aliphatic carbon atoms.

2. The lubricating grease according to claim 1 wherein the said lubricating oil is a mineral oil.

3. A lubricating grease consisting essentially of a mineral lubricating oil thickened to a grease consistency with a sodium alkyl mercapto fatty acid salt having the formula RSR COONa, wherein R is a straight chain alkyl group containing about 8 0t carbon atoms and R is an alkylcne group containing from 1 to 5 carbon atoms, and wherein R and R together contain at ieast about 11 aliphatic carbon atoms.

4. The lubricating grease according to claim 3 containing about 15-45 percent by weight of the said salt.

5. A lubricating grease consisting essentially of a mineral lubricating oil thickened to a grease consistency with about 15-45 percent by Weight or"; sodium lauryl mercapto propionate.

6. The lubricating grease according to claim 5 wherein the said mineral lubricating oil has a Viscosity in about the range 600 seconds SU viscosity at 100 References Qited in the file of this patent UNITED STATES PATENTS 2,216,751 Rosen Oct. 8, 1940 2,567,023 Morway et al Sept. 4, 1951 2,892,852 Koenig et al June 30, 1959 OTHER REFERENCES Boner: Manufacture and Application of Lubricating Greases, Reinhold Publ. Corp, N.Y., 1954, pages 485 546 and page 573. 

1. A LUBRICATING GREASE CONSISTING ESSENTIALLY OF A LUBRICATING OIL THICKENED TO A GREASE CONSISTENCY WITH A SODIUM ALKYL MERCAPTO FATTY ACID SALT HAVING THE FORMULA RSR1COONA, WHEREIN R IS A SUBSTANTIALLY STRAIGHT CHAIN ALKYL GROUP CONTAINING ABOUT 8 TO 20 CRBON ATOMS AND R1 IS A STRAIGHT CHAIN ALKYLENENE GROUP CONTAINING FROM 1 TO 5 CARBON ATOMS, AND WHEREIN R AND R1 TOGETHER CONTAIN ABOUT ALIPHATIC 11-30 ALIPHATIC CARBON ATOMS. 